Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $101.63   12.677%   $114.5136   $114.51   $114.50   $114.50  
  Purchase #2 $108.46   4.592%   $113.4405   $113.44   $113.45   $113.40  
  Purchase #3 $50.64   11.419%   $56.4226   $56.42   $56.40   $56.40  
  Purchase #4 $73.61   11.305%   $81.9316   $81.93   $81.95   $81.90  
  Purchase #5 $236.36   7.752%   $254.6826   $254.68   $254.70   $254.70  
  Purchase #6 $104.36   3.480%   $107.9917   $107.99   $108.00   $108.00  
  Purchase #7 $74.43   3.380%   $76.9457   $76.95   $76.95   $76.90  
  7 purchase totals = $749.49       $805.9283   $805.92   $805.95   $805.80